Scientists Find Method to Quantify One-Way Einstein-Podolsky-Rosen Steering

  • [2016-05-20]
  • A recent study conducted by Key Laboratory of Quantum Information of University of Science & Technology of China (USTC) of Chinese Academy of Sciences (CAS) reported a way to quantify the one-way Einstein-Podolsky-Rosen (EPR) steering in a two-qubit system. The study was published on Physical Review Letters.

    Einstein-Podolsky-Rosen (EPR) steering describes the ability of one observer to nonlocally “steer” the other observer’s state through local measurements. EPR steering exhibits a unique asymmetric property; i.e., the steer ability can differ between observers, which can lead to one-way EPR steering in which only one observer obtains steer ability in the steering process. This property is inherently different from the symmetric concepts of entanglement and Bell nonlocality.

    For instance, Alice and Bob are both observers and share entangled states. There are cases in which the ability of Alice to steer Bob’s state is not equal to the ability of Bob to steer Alice’s state. There are also situations in which Alice can steer Bob’s state but Bob cannot steer Alice’s state, or vice versa. These situations are referred to as one-way steering. This distinguished feature would be useful for the one-way quantum tasks. One-way EPR steering has been realized in the continuous variable system with restricting to the Gaussian measurements.

    Researchers experimentally realize one-way EPR steering using the general measurements in the entangled two-qubit system. They propose an intuitive criterion called as “steering radius” to quantify the ability of EPR steering. The local hidden state model, which provides a direct and convinced contradiction between the nonlocal EPR steering and classical physics, is constructed to reproduce the experimental results obtained in the failed EPR steering process. Also, the asymmetry is still demonstrated to exist in two-way EPR steering because the values of each side’s steer ability are different.

    The results provide an intuitive perspective for understanding one-way EPR steering and the asymmetry of quantum non-locality. They are significant within quantum foundations and quantum information and show the potential applications in one-way quantum information tasks. It was mainly conducted by the research group led by Prof. LI Chuanfeng and Prof. XU Jinshi at Key Laboratory of Quantum Information and they cooperated with Nankai University through the experiment.

    This work was supported by the National Natural Science Foundation of China, the Strategic Priority Research Program (B) of the Chinese Academy of Sciences, the Fundamental Research Funds for the Central Universities, Program for New Century Excellent Talents in University, Science foundation for the excellent PHD thesis, the Youth Innovation Promotion Association and Excellent Young Scientist Program CAS, and the National Basic Research Program of China.


    Figure: Illustration of one-way EPR steering (Image by USTC)